Electric heater.



F. W. HEWITT.

ELECTRIC HEATER.

APPLICATION mu) MAY 21. me.

1 ,23 8 ,727 Patented Aug. 28, 1917.

x f I 9 1 7/ I/ I! 11, g i) 6 5 4 heating devices.

UNITED STATES FRANK WALDO HEWITT, 0F ARLINGTON,

PATENT OFFICE.

MASSACHUSETTS, ASSIGNOR TO SIMPLEX ELECTRIC HEATING COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A CORPORA- TION OF MASSACHUSETTS.

ELECTRIC HEATER.

Application filed May 27,

To all whom it may concern:

Be it known that I, FRANK WALDO HEwrrr, a citizen of the United States, and resident of Arlington, county of Middlesex, and State of Massachusetts, have invented an Improvement in -Electric Heaters, of which the following description, in connection with. the accompanying drawings, is a specification, like letters on the drawings representing like. parts.

My present invention is an electrical heating device. and the object of the invention is to improveand-perfect such electrical lnutilizmg as. expensive a heating element as electricity it is of great importance to conserve theienergy and to supply as high avdegree of heat as is possible, together with a system or apparatus which will insure long life to the heater. Heretofore electric heatersin such devices as are commonly employed 'n domestic use have been built in two distinct ways. Either the heat generated in the heating element was transmitted to the surface being heated, by conduction,.orthe heat was dissipated from the heat generating body by radiation.

The first of these'methods involves a construction whereby the heat generated must pass through a heat insulating substance to get to the part being heated. This is an unnatural path for heat to travel, and in order to force it to travel such a path there must be a substantial difi'erence in temperature between the heating element and the part being heated. This results in developing a high temperature on the element if the paid; being heated is brought to a temperature that is sufficiently hot for general utility purposes, and is objectionable, rapidly d teriorating and oxidating the heating element.

The second system of heating by radiation from the heating element has heretofore been used by supporting the heating element in a grooved member-this member being of electrically insulating material. and consequently of heat insulating material. The usual'practice is to place a coiled wire in the grooved member-thus permitting the heat to radiate, but only from a limited area of the coil. The inability to dissipate its heat freely on all sides results in the heater attaining a higher temperature than if the Specification of Letters Patent.

Patented Aug. 28,1917.

1916. Serial No. 100,331.

material surrounding the coil were of a nature that would conduct the heat away as generated, and therefore this second method is also objectionable and unsatisfactory.

It is a principle of natural phenomena that as the temperature of a body increases the heat dissipated from that bodyby means much larger ratio, a red heat a very large percentage of its heat by radiation, and my present invention takes advantage of this principle. @1 0 I make use of the further principle whereby the heat thus radiated is quickly absorbed and conducted away, withthe the temperature of the wire isrelieved on all sides, and very quickly after generated, thus insuring long life to the, heating. element. v

In 'my system the heat generating element is practically surrounded closely or 1;allsides by heat conducting material, and the. only obstruction to the flow of heat from this heat generating element to the part being heated is a very sma entirely free of obstruction by any .physica substance through practically the entire length of the coil.

As in practice the heating element is operating at a red heat or somewhat higher, as stated above, the natural way for it to dissipate its heat under this condition is by radiation, consequently the coil as supported in my system is in a condition that is much more favorable to taking heat away quickly from the heating element than in either of those above mentioned.

This permits the dissipation of heat from the element without its attaining an excessive temperature, and thus durability of the element is assisted. Inasmuch as the heat conducting material is in very close proximity to the heating element, I am enable to reduce the temperature difference between the heater and the part being heated, and to raise the heating surface of the heater substantially to the same degree of heat as that of the heating element itself.

A further feature oi the invention is in its mechanical arrangement to permit easy and simple assembly by unskilled labor, an to result that is rigid and it dissipates in a construction durable, and in no sense fragile.

In carrying out my invention 1 may utiresillt,,that

lize a softcast iron heater plate, which is an excellent heat conducting material and by arranging the heating wires in close thermo-proximity while still maintaining the same electrically separated by a suitable air space, the cast iron will readily absorb the heat radiated from the wires and conduot -sa id heat ,to-the working surface of the heater. Thus the life of the resistance wires is greatly increased byfreeing themselves of heat, quickly, from every point, excepting at a minimum of supporting points. To support the heating element in position I prefer to use thin sheets of mica or the like, slotted to receive the resistance wire or coil of wires and arranged transversely of the wires, so as to occupy a minimum amount of space and not interfere with the free'heat radiation therefrom. I also arrange the heating wires, if in the form of coils as'preferred, so that the continuity of the wire from one coil to another is unbroken. irrespective of the change in dime-- tion 'of the coils.

Further important advantages, features of the invention, details of construction and novel combinations will be hereinafter more fully pointed out andtlaimed.

Referring to the drawings illustrating a preferred embodiment of the invention lhgure 1 is a view in'perspective of the under-side of agrooved heating plate with the cover removed;

Fig. 2 is an'enlarged fragrnental crosssectional view of one edge of theheater;

*ig. 3 is'a fragmentary view of the mica insulating and supporting arrangement;

Fig. 4 1s a view of the arrangement at the end of two adjacent coils, showing *thebontinuity of the resistance wire from one coil to another;

Fig. 5 is a plan :view of said coils and their connections at each end; and

Fig. 6 is a cross sectional, fragmentary view of a heater and mice. insulating supports in the groove construction with a plurality of heating coils.

It. will be understood that I may utilize a heating plate of any desired size, shape or contour, such as round, square or the like, the usual electrical heating device in stores for domestic use being square or round, and I have illustrated my invention with a reclan ular heater.

l form the mating device 1 of cast iron, with a smooth top 2 or utensil-receiving surface, which is the working surface of the heater and on which the article to be heated is placed. The under-side of the heating device 1 is cast with a plurality of grooves 3 and alternating ribs 4 of suitable depth and diameter to receive the coils of the heating wires to be applied therein. 1 Mil, cast or mill across the ribs 4 slots at suitable points to receive the insulating ma- .to the entire heater and position to cooperate with terial, preferably mica, or the like, 6, arranged to support the coils 5 in predetermined position within the grooves 3. I prefer to leave the outer sides and ends of the heating device 1 rigid toimpart strength and prevent warping of the top plate or working surface 2. The ribs 4 also prevent such warping,-but are somewhat weakened by the transverse slots to receive the insulating element 6. These slots are of ust suflicient width to receive the thin sheets 7 and 8 of mica, which may be forced or jammed therein. The mica sheets are fitted with cooperating grooves 9 in the top sheet 7 and 10 in the lower strip 8, which grooves are of suitable depth each other in holding the heating coils in desired position relatively to the depth of the grooves 3. Preferably I soar-range the mica insulating supporting strips '7 and "8 that the heatingcoils'S will be sustained almost at the extreme bottom of'the'grooves 3 and in as cl'ose thermo proximity to the undersurface of the top 2 as can safely be attained without sai'd actually ftouching the cast'iron: =As-the-heattfrom the coils 5 is radiated in all directions, this construction enables the he'ating ooil to be substantially surrounded y the'heat oonduo'tin iron of the top 2 and ribs 4, conserving afi of such heat and fiurtheraidin the-free d.issi ation of hat from the tlierapid absorptionand conduction to t 2. To still =further conserve the heat I-adiated from the coils 5,"whichwould otherwise escape froni-the open mouths-ofthe grooves 3,- I' afljix a cover 11, referably of metal, over the under-side ,of the heating device 1, attaching the same thereto by screws 12 at suitable 'points around the heater. I ma also-prefer to do the heat insulating pac 'ng by mineral wool or the like under the cover 11, and inclose the same by a thin metal sheet 14, illustrated in fragmentary form in Fig. 2, securin the latter by bolts 15 to a flange 16 on "the eating device 1.

If desired, a plurality of heating coils may be fitted within the rooves 3 as indicated in Fig. 2 by the additional coils 17, in which construction an intermediate mica plate 18, having top and bottom slots 19 and 20 respectively, is provided, to coope'rate with additional mica sheets 31 and 22 corresponding to the strips 7 and S of Fig. 3 'to hold the heating coils 5 and 17 spaced from each other and from the ribs 4 and heating device 1L It is very desirable that the continuity of a resistance'wire, such as the heating coils 5. should not be broken, even when a change of direction in the wire is necessary, the breaking of such wires and carrying the current through soldered joints over other e w rki ig surface wires or difi'erent mechanical means, is BX- pensive and an unsatisfactory construction. Such soldered joints ,are apt to break through constant temperature changes, because of the concentrationof heat, prevent uniform flow of current, induce oxidation, and present a weak and unsatisfactory construction. I obviate-these difliculties by having the coils connected by inte ral wires 23, see Figs. 4 and 5, whichwill ie in grooves 24, one at the bottom of the coils which it connects, as, for example, 25 and 26, and the other leadingfrom the top of the adjacent coils which it connects, 27 and 28. This arrangement enables me to keep all the heating coils 5 in the same plane and yet connect them by the short portions 23 with the latter spaced apar and joining alternate coils This also is advantageous in enabling the usual three heat construction of an electrical heater to be obtained, supplying two circuits through the heater, the circuits designated as A and B being capable of use single, in series or multiple, thus, fulfilling the usual requirements for electrical stove use.

My improved electrical heater is capable of very easy assembling, without special fittings, screws, tools or skill. The plate 1 of cast iron or other desired heat-conducting material may be roughly cast to form, the slots milled out or cast for the insulating elements and then a lower mica strip 8 (or 22 when the form shown in Fig. 6 is utilized) is fitted within each of said slots, said strip being referably equal in length to the width of t e heater, the heating device 1 being inverted with the grooved side uppermost to facilitate this assemblin The end mica strips, shown in Fig. 4, also include the top member 29, intermediate strip 30 and lower strip 31, grooved as shown in said fi ure, the lowermost strip 31 being similar y positioned in the end slots. The heating coils 5 are then laid in position, resting on the slots 10 of the lower supporting mica strip 8, and the second or top member 7 bein then forced into posi tion as shown in Fig. 3, wedgin with the member 8 into the slot out there or. Similar operation at the ends where the connecting sections 23 are to be fitted, is also performed, the wedging action of the insulating strips serving to hold the wires and said strips in assembled position. The bottom plate 11 is then fitted, and the packing 13 and cover 14 applied, the heating device 1 reversed with the top plate 2 uppermost and terminals 32 and 33 connected at the end of the circuits A and B respectively.

The electrical heater just described illustrating a preferred embodiment of the invention, is to be understood as being shown for illustrative purposes onl and not to limit my invention thereto. The invention however, is

eculiarly applicable to the type of grooved eater herein shown and described, and enables each heating coil to be supported with a minimum of insulation, i. e., the thin edge of the mica strips, between the coils and the heat conducting material of the to 2.

My invention is further describe anddefined in the form of claims as follows:

1.,An electrical heating device comprising a heat conducting plate formed with a plurality of parallel rooves anddepending heat conductm POItlODS of said plate, constituting thesi es of the grooves, resistance coils suspended in each groove in substantially equal thermo-proximity to the, sides and bottom of said groove, but electrically insulated therefrom by an airspace, insulating supporting means for said coils at spaced intervals in each groove.

2. An electrical heating device comprising a heat conductin plate formed with a; plurality of paralle; grooves, resistance. coils suspended ineach roove in; close thermoproximity to the si es and bottom of said oove, but electrically insulated therefrom y. anair space, and mechanical insulating supportin means wedging said wires against isplacement longitudinally and spanning the grooves at spaced intervals and holding the resistance coils in said airspaced relation.

3. An electrical heating device com rising a heat conducting plate formed with a plurality of parallel grooves, resistance coils suspended in each oove in close thermoproximity to the si es and bottom of said 'roove, but electrically insulated therefrom by an air space, and slotted mica sheets scoured to said plate and spanning said grooves constituting a mechanical insulating support for the resistance coils to hold them suspended in said ooves.

4. An electrical eating device, comprising a heat conducting support having a plurality of parallel grooves, a resistance element suspended in each groove and insulated by an air space from the support, and insulating means holding said resistance elements suspended in said grooves, said insulation being spaced longitudinally of the resistance elements and comprising thin overlapping mica sheets.

5. An electrical heating apparatus, comprising a heat conducting plate having a plurality of parallel grooves, a resistance element suspended in each roove, and insulating means holding said resistance elements in said grooves and air-spaced therefrom, said insulation consisting in a plurality of slottedsstrips spaced longitudinally of the resistance elements and interlocking with said resistance elements and with the sides of the walls forming the grooves to hold the resistance elements suspended in said grooves.

f6flllii electrical heating apparatus, cmprising a heat conducting plate having a pluralrty of paralle'l grooves, a plurality of resistance elements-in vertical a-linem'ent and sp'aced'e ually from the sides of each groove, andinsulatingmeans holding said resistance clexnei'rtsdn said grooves and air-spaced therefroniandfrom-each other, said insulationlbein spaced longitudinally of the resistance' clients.

' 7; An electrical heating apparatuaincluding 'a'hat conducting'member formed with a"smoofth surface on one side and a plubf grooveson the other side, each groo'veheing adajited to receive a resistance element of slightly less diameter than the cross sectional area of said roove, means to hdld the resistance element 1n each groove in close thefmo proximity' to the sides and botto'hi'off the groove; but electrically insulated uherefmmt an air space and at spaced"ihtervafls-l1y insulating means supthe partitions forming said was a mu: amma? 'be dhtalned m grooves and adapted to en age the resistance element at spaced intervals.

8. An electrical heating a paratus, including a heat conducting memller formed with a smooth surface on one side and a. pinrality of grooves on the other side, each groove being adapted to receive a resistance element, means to hold the resistance element in each groove in close theme-proximity to the si es and bottom of the groove, but electrically insulated therefrom at spaced intervals by insulating means adapted to be wedged in transverse slots across the partitions forming said grooves and supporting the resistance elements at spaced intervals.

In testimony whereof, I Have signed 1113* name to this specification, in the'presence of I witnesses. NK WALDO two subscribin 4 F "Witnesses:

AGNES B. Gmrrm, James L. MAHER.

five cents each, by addressing the c'ommissloner '0! Intent; Washington, D. C." t 

